Complex oxide materials represent one of the most promising frontiers for realizing multifunctional devices that address pressing global challenges in energy efficiency, sustainable electronics, and emerging quantum technologies. These materials uniquely combine diverse functional properties – such as superconductivity (SC), ferroelectricity (FE), and ferromagnetism (FM) – within a single crystalline framework. Traditionally, many of these properties were thought to be mutually exclusive due to their antagonistic physical origins. However, recent breakthroughs in materials synthesis, nanoscale interface engineering, and strain control have demonstrated that such properties can not only coexist but also couple in ways that generate entirely new functionalities. In particular, the interplay between SC and FE has garnered significant attention in the condensed matter and quantum materials community. While bulk SrTiO3 (STO) has served as a model system for exploring this coexistence, practical device applications remain limited because conventional bulk doping renders the entire crystal conducting, eliminating the possibility of electric-field control over the electronic phases. This constraint is a major barrier to realizing tunable, low-power quantum devices based on the SC–FE coupling. Recently, it has been shown that two-dimensional electron gases (2DEGs) formed at carefully designed oxide interfaces can exhibit ferroelectric ordering while remaining highly conductive, offering an unprecedented platform to electrically modulate superconducting properties. However, only a handful of systems – most notably LaAlO3/Ca-doped STO – have shown experimental signatures of both FE and SC coexisting at the interface, and even these do not display the anticipated enhancement of the superconducting transition temperature. This underlines the urgent scientific need to discover, engineer, and understand new oxide 2DEG systems that can unlock the full potential of SC–FE coupling.
The SURFER project directly addresses this knowledge and technology gap by moving beyond bulk-doped oxides to design and fabricate oxide heterostructures that host robust, switchable 2DEGs with coupled superconducting and ferroelectric properties. By leveraging state-of-the-art thin-film deposition techniques, atomic-scale interface engineering, and epitaxial strain tuning, SURFER will pioneer new pathways for manipulating quantum states in low-dimensional systems. Specifically, the project will systematically investigate three underexplored but promising oxide platforms: (1) strained SrTiO3 (STO), where epitaxial strain can stabilize ferroelectricity; (2) BaTiO3 (BTO), a well-known robust ferroelectric whose single-domain structure can be precisely controlled through strain; and (3) Nb-doped KTaO3 (KTN), which combines emergent superconductivity with strong spin-orbit coupling, offering an additional handle for quantum functionality. To create high-mobility 2DEGs in these systems, SURFER will implement two complementary approaches: (a) deposition of reactive metals to induce redox-driven carrier formation at the oxide surface, and (b) growth of polar ABO3 oxides to trigger electronic reconstruction at the interface. The overarching objectives of SURFER are to discover new material systems that support tunable SC – FE coupling, unravel the underlying physical mechanisms that link these phases, identify routes to enhance superconducting transition temperatures through ferroelectric ordering, and develop strategies for electric-field control of superconductivity in 2DEGs. The insights gained will advance fundamental understanding at the intersection of quantum materials, oxide electronics, and interface physics.
By doing so, SURFER aligns with the European Union’s strategic goals under the Green Deal and Quantum Technologies Flagship, paving the way for future generations of energy-efficient, multifunctional devices such as ultra-low-power switches, quantum sensors, and reconfigurable superconducting circuits. In the longer term, these advances could have far-reaching impacts on information processing, secure communication, and sustainable digital infrastructures. In addition to its scientific and technological ambitions, SURFER integrates social sciences perspectives to assess the societal readiness and potential ethical implications of these emerging quantum technologies, ensuring that the breakthroughs are developed responsibly and with public trust.
In summary, SURFER sets the scene for a new class of oxide-based quantum materials with controllable multifunctional properties, strengthening Europe’s leadership in advanced functional oxides and positioning European research and industry at the forefront of the next technological revolution.
